1. Field of the Invention
The present invention generally relates to image forming apparatuses, control methods of the image forming apparatuses, and printing medium conveyance apparatuses. More specifically, the present invention relates to an image forming apparatus where printing is performed on a printing medium (sheet) conveyed at a conveyance path, a control method of the image forming apparatus, and a printing medium conveyance apparatus.
2. Description of the Related Art
Conventionally, a detecting part is provided in an image forming apparatus such as a copier or printer so that conveyance of a sheet as a printing medium is detected or a control timing of the apparatus is determined. For example, an optical sensor or a feeler sensor configured to detect arrival of the sheet, as the detecting part, is provided in the way of a sheet conveyance path. In addition, it is normal practice that the sheet is detected in order to 1) confirm if the sheet conveyed from a printing medium receiving part passes a designated position of the conveyance path, 2) determine a conveyance timing of a next sheet, 3) detect a sheet jam, or 4) confirm that there is no sheet just after the sheet is detected by the detecting part.
Furthermore, in the above-mentioned image forming apparatus, if noise is superimposed on a detecting signal from the detecting part, it cannot be determined which detecting signal is an original one detecting the sheet so that an error in detection may be made. In order to prevent such an operational error, a masking process is applied to a detecting signal until a designated time set in advance passes during which the sheet received in a printing medium receiving part (tray or cassette) is conveyed. By stopping the masking process just before the sheet arrives at the detecting position, the reliability and likelihood of the detecting signal is improved. A phenomenon where the noise is superimposed on the detecting signal can be found, for example, when foreign matter other than the sheet comes in contact with the feeler sensor provided as the detecting part or foreign matter such as a broken piece of the sheet is adhered on a lens of the optical sensor provided as the detecting part.
In the above-mentioned masking process, it is possible to prevent the error in detection due to the noise, by cancelling the detecting signal being output from the detecting part from when no sheet provided at the conveyance path is detected to when a designated time passes. See, for example, Japanese Laid-Open Patent Application Publication No. 3256043.
In addition, the detecting signal from the detecting part configured to detect the sheet is used as, for example, a trigger for performing a printing job or a timing signal for switching a clutch for starting motor driving or turning on or off motor torque.
In the meantime, in the image forming apparatus, an emergency stop may be required when the sheets are continuously conveyed and printing is performed. Emergency stop is required, for example, in a case where the sheet jams at the conveyance path, a head end of the sheet is bent, or a printer cover is opened. In the image forming apparatus, when a case among the above-mentioned cases requiring the emergency stop is detected, the emergency stop of the sheet conveyance is done by turning off the motor of the conveyance apparatus configured to convey the sheet or disengaging the clutch configured to transmit a rotational driving force of the motor to a sheet feeding roller.
However, in the image forming apparatus, if the masking process is performed after the sheet conveyance restarts in a case where the emergency stop is made as well as a normal printing step being performed, the printing likely restarts from a state where the sheet sticks out from the printing medium receiving part. Accordingly, even if the sheet arrives at the detecting position where the detecting part can detect the sheet, the sheet may not be detected because the masking process is not applied.
In addition, the detecting signal of the detecting part can be a trigger for starting a printing job relative to the sheet conveyed from the printing medium receiving part. Therefore, if the original detecting signal is disregarded due to the masking process, printing cannot be performed on the sheet so that only conveyance of the sheet may be performed.